[wdemere]

The main compartment of the tube is made about 1 or 1.5 inches higher than the film's top edge when fully inserted (film is inserted long side vertical). This would allow one to fill the tube with developer and have the film lying about half and inch or so below the water level. Screw on the tube cap and start the development procedures accordingly.

I'm pretty sure that BTZS tubes (at least the 4x5 tubes I have) are NOT made this way. You must agitate fairly often (roll every 10-15 seconds at the least) or you get nice lines on your negative. I get this effect even when overfilling the cap as much as possible. Though I suppose you could fill the entire tube with developer if you wanted, but that defeats the convenience/purpose of the cap.

Just a warning to those who might try it....